In some embodiments, apparatuses and methods are provided herein useful for sensing pressure. In some embodiments, miniature housings are manufactured at ends of optical fibers. In some embodiments, a diamond diaphragm is provided on a hollow housing that receives a fiber optic cable and is sealed to form a Fabry-Perot cavity. In some forms, a plurality of sensors may be manufactured in batch.
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7. A method of manufacturing a sensor, comprising:
depositing a diamond film layer on a first side of a silicon substrate;
etching a cavity in a second side of the silicon substrate, the cavity extending from the second side of the substrate to the diamond film layer;
disposing a cable within the cavity at the second side of the substrate; and
joining the optical cable to the silicon substrate with at least one adhesive.
1. A sensor comprising:
a housing having a cavity extending from a first end of the housing to a second end of the housing;
a diamond diaphragm extending across the cavity at the first end of the housing; and
an optical cable disposed in the cavity at the second end of the housing;
wherein the optical cable is mounted to the housing with a uv curable adhesive and a ceramic adhesive, and
wherein the housing comprises silicon.
15. A sensor comprising:
a housing having a cavity extending from a first end of the housing to a second end of the housing;
a diamond diaphragm extending across the cavity at the first end of the housing;
an optical cable disposed in the cavity at the second end of the housing; and
an anti-oxidation barrier disposed on a side of the diamond diaphragm opposite the housing structure;
wherein the optical cable is mounted to the housing with a uv curable adhesive and a ceramic adhesive.
17. A sensor comprising:
a housing having a cavity extending from a first end of the housing to a second end of the housing;
a diamond diaphragm extending across the cavity at the first end of the housing;
an optical cable disposed in the cavity at the second end of the housing; and
a heat transfer device in contact with the diamond diaphragm;
wherein the optical cable is mounted to the housing with a uv curable adhesive and a ceramic adhesive, and
the heat transfer device comprises silicon carbide or tungsten.
11. A method of manufacturing a plurality of sensors, the method comprising:
depositing a diamond film layer on a first side of a silicon substrate;
etching the diamond film layer to form a plurality of separate diamond film areas;
etching a plurality of cavities in a second side of the silicon substrate, the each of the plurality of cavities located opposite a diamond film area, the cavities extending from the second side of the substrate to the diamond film areas;
disposing a plurality of optical cables within the cavities at the second side of the substrate, with one cable per cavity; and
joining the optical cables to the cavities with at least one adhesive.
3. The sensor of
4. The sensor of
5. The sensor of
8. The method of
9. The method of
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14. The method of
16. The sensor of
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This application claims the benefit of U.S. Provisional Application No. 62/688,039, filed Jun. 21, 2018, which is hereby incorporated herein by reference in its entirety.
This invention relates generally to sensors, particularly fiber optic pressure sensors.
Interest in the use of miniature fiber-optic pressure sensors for medical and industrial applications has progressively increased over the recent decades due at least in part to their unique attributes such as ultra-fast dynamic response, micro-scale size, high sensitivity, immunity to electromagnetic interference, and the convenience of light transmission/detection through optical fibers. The compact dimensions of the fiber-optic sensors significantly improve the spatial resolution of measurements and, in the case of medical applications, patients' comfort level. Various types of miniature optic sensors reported in the literature are based on the Fabry-Perot optical cavity. An extrinsic Fabry-Perot (FP) cavity is formed at the tip of an optical fiber by using the end of the optical fiber surface and a reflective miniature diaphragm built on a support structure. The diaphragm deflects in response to variations of ambient pressure and causes changes in the interference signal generated by the FP cavity.
Fiber optic sensors has been widely used for various applications such as chemical, acoustic, pressure, strain, and temperature sensing due to their EMI inertness, high sensitivity, high bandwidth, small form factor, and general robustness of sensor structures.
Single crystal sapphire has been identified as a sensor material for high temperature sensing due to its high melting temperature (i.e. 2040° C.). However, fabrication of sensors with sapphire requires polishing and high temperature fusion splicing using high power laser, which are generally costly procedures. In addition, the temperature sensitivity of fiber optic pressure sensors presents a drawback in terms of accuracy of the measured parameter, particularly when measuring pressure.
There remains a need for improved sensors that are capable of operating accurately under a wide variety of conditions.
Diamond-based sensor are provided for measurement of variables at various conditions. In some forms, a diamond diaphragm is mounted across a cavity of a hollow housing. The diaphragm may be mounted to the sensor housing by fusing diamond material of the diaphragm to the housing (in some embodiments by depositing or growing the diaphragm material directly onto the housing) or by coupling the diaphragm and housing with adhesive, such as a ceramic adhesive. In one form, a sensor has a silicon housing coupled to both an optical cable and a diamond diaphragm. In some forms the fabrication of the sensor is scalable using a batch process for the diamond diaphragm and sensor housing structure and an automated fiber insertion and mounting process.
In some forms, the housing of the sensor may be generally cylindrical with a generally cylindrical cavity formed therein extending from a first end to a second end of the housing. One end of the housing may be covered by a diamond diaphragm structure, such as a polycrystalline diamond layer, while the opposite end of the housing may receive an optical cable. The optical cable may be, for instance, fiber optic cable of various diameters, sapphire optical cable, or other suitable optic cable. In some forms, one or both ends of the housing cavity are sealed with one or more adhesives. In some forms, both polymer and ceramic adhesives are used to secure the optical cable to the housing. In such a two-adhesive system, the polymer adhesive provides air-tight sealing of the sensor cavity and the ceramic adhesive ensures a good linearity of pressure sensing. An anti-oxidation barrier may be provided over the diaphragm, for instance a layer of titanium oxide, silicon oxide, aluminum oxide, or combinations thereof.
Sensors of the type described may be low-cost and highly accurate with improved chemical resistance and temperature resistance, and can be of benefit in a variety of fields such as biomedical sensing and industrial sensing.
A method of manufacturing one or more sensors may in some forms comprise depositing a diamond film layer on a first side of a substrate, etching a cavity in a second side of the substrate, the cavity extending from the second side of the substrate to the diamond film layer, disposing a cable within the cavity at the second side of the substrate, and joining an optical cable to the substrate with at least one adhesive. These processes may be performed in batch to simultaneously manufacture a plurality of sensors at one time. For instance, a batch of at least 100 sensors may be formed essentially simultaneously in an automated process. Depositing the diamond film layer may comprise a hot filament chemical vapor deposition in some embodiments. Etching of the cavity or cavities in the silicon comprises deep reactive ion etching. The method may further comprise, pursuant to certain embodiments, joining an optical cable to the substrate by applying a UV-curable adhesive to the optical cable, subjecting the UV-curable adhesive to ultraviolet radiation when the UV-curable adhesive is in contact with the optical cable and the substrate in an amount effective to cure the UV-curable adhesive, and applying a ceramic adhesive to the UV-curable adhesive.
Disclosed herein are embodiments of systems, apparatuses and methods pertaining to sensors including a deflectable diamond diaphragm. This description includes drawings, wherein:
Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. Certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. The terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.
Generally speaking, pursuant to various embodiments, systems, apparatuses and methods are provided herein useful to provide a high temperature pressure sensor containing a diamond diaphragm, such as a diaphragm comprising heteroepitaxial polycrystalline diamond film. In some forms, the sensor is composed of a polycrystalline diamond diaphragm that covers a cavity structure of a housing made from silicon or other materials. In some forms, a sensor comprises a housing structure having a cavity extending from a first end of the housing to a second end of the housing a diamond diaphragm extending across the cavity at the first end of the housing and an optical cable or fiber disposed in the cavity at the second end of the housing, wherein the optical cable is mounted to the housing with a UV curable adhesive and a ceramic adhesive. In some forms, the housing comprises silicon. In some forms, the diamond diaphragm comprises polycrystalline diamond. In some forms, the sensor further comprising an anti-oxidation barrier disposed on a side of the diamond diaphragm opposite the housing structure, the anti-oxidation barrier comprising one or more layers of titanium oxide, silicon oxide, aluminum oxide, or combinations thereof. In some forms, the fabricated sensors can be used in temperatures up to 1700° C. in non-oxygen environments.
Polycrystalline diamond advantageously has high manufacturability, high mechanical strength, and high thermal conductivity. In some forms, diamond films can be grown in wafer scale, providing good control over thickness. Additionally, diamond layers can be patterned using conventional photolithography and reactive ion etching processes. In some forms, an oxidation barrier is provided to protect the diamond diaphragm in order to improve operation of the sensor in an oxygen rich environment. A Fabry-Perot cavity is formed between the tip of the optical fiber and the diaphragm. The diaphragm deflects in response to variations of ambient pressure when the opposite end of the cavity is sealed, causing changes in the interference signal generated by the Fabry-Perot cavity which are then transmitted along the optical fiber.
In some forms, polycrystalline diamond can be grown by chemical vapor deposition (CVD). Polycrystalline diamond has many unique properties which can be exploited as a sensor material for various sensing applications. Chemically vapor deposited polycrystalline diamond films have outstanding properties of high Young's modulus (for instance, about 1,143 GPa in some forms), low thermal coefficient of expansion (about 1-1.5 ppm/° C. in some forms), high melting temperature (in some forms above 1700° C. in a vacuum or oxygen free environment), ultra-high thermal conductivity (about 2200 W/cm K in some forms), and inertness to most acids and bases.
A fused silica optical fiber is attached to the cavity of the sensor in some embodiments, and in particular embodiments attachment of the diamond diaphragm and/or optical fiber to a sensor housing is accomplished with high temperature ceramic adhesive, a polymer adhesive, or a combination of.
In some forms, the sensor may further comprise a heat transfer device in contact with the diamond diaphragm to assist in removing or redirecting heat applied to the diamond diaphragm, especially in sensors for use in high-temperature environments. In some embodiments, the heat transfer device may comprise one or more cylindrical heat sinks disposed about the sensor housing. In some embodiments the heat transfer device may comprise silicon carbide or tungsten.
The inner diameter of the cavity 103 in most embodiments will be slightly larger than the optical fiber 101 to assist in insertion of the fiber and to accommodate adhesive between the fiber and inner walls of the housing 102, and to account for tolerances in cavity formation techniques, tolerances in fiber formation, and tolerances for fiber assembly. For instance, the distance between inner walls of the housing may be, in some embodiments, about 5-15 μm greater than the diameter of the cable, preferably about 10 μm. For instance, the housing may in some embodiments had a cylindrical passage from one end to the other having a diameter of 135 μm for use with commercial optical fiber having a diameter of 125 μm.
The thickness of the diamond layer may be designed to meet the specific pressure sensitivity and maximum pressure ranges, preferably while ensuring a linear sensor response. For instance, in some forms the thickness of the diamond diaphragm may be designed to give a deflection of about 10 nm/psi or higher and to operate at a pressure of 30 psi or higher. In some forms, the thickness of the diamond diaphragm may be about 1.1, 1.2, 1.3, 1.4, or 1.5 μm, or may be thicker for higher temperature sensing. For applications where lower pressures will be detected, the diaphragm may be thinner, while thickness can be increased for use in higher pressure ranges. The addition of an anti-oxidation layer decreases the sensor pressure sensitivity and increase the maximum pressure range. When the diamond diaphragm is relatively thin (for example, 1 micron or less in thickness), the effect of the anti-oxidation layer is more significant. However, if the diamond layer is relatively thick (for example, 3-4 microns), the effect of the anti-oxidation layer is relatively small.
Optionally, a heat sink may accompany the sensor in order to dissipate heat and relieve strain on the diaphragm of the device. Referring to
The sensor fabrication process shown in
As shown in step (b) of
Steps (c) through (f) of
In step (d), when a desired gap distance between the optical fiber and the diamond diaphragm is obtained, a small drop of polymer adhesive, in the illustrated example a UV-curable adhesive, is applied between the fiber and silicon cavity inlet to fix the fiber and seal the formed optical cavity 503 to form a chamber constituting a Fabry-Perot structure. The adhesive may be a cross-linked UV curable polymer. Due to capillary effect, the gap between the cavity wall and the optical fiber is filled.
In step (e) of
In step (f), a second adhesive 508, for instance metal or ceramic adhesive, is applied on top of the polymer adhesive 506, and cured. In some instances, the second adhesive 508 is subjected to heat in order to effect curing. The addition of the second adhesive stabilizes the structure and reduces movement of the fiber 505 relative to the sealed optical chamber 509, significantly improving the linearity of pressure and temperature response by minimizing the viscoelastic behavior of the UV curable polymer.
As shown in
The optical signal reflected from the sensor 701 is composed of three inference signals from three different optical interfaces. There are interferences among these three signals and a superimposed interference spectrum is observed from the fabricated sensors. A representative sensor spectrum is shown in
A sensor was fabricated by i) growth of a diamond diaphragm layer on a silicon wafer, ii) fabrication of an optical housing structure by removing portions of the silicon wafer, and iii) optical fiber alignment and mounting within the optical housing.
The first step involved growing the diamond layer on the silicon wafer. A 1.2 μm thick heteroepitaxial diamond film was formed in a hot filament chemical vapor deposition (HFCVD) system on single side polished p-type silicon wafers. After cleaning and then removing the surface oxide, the silicon wafers were sonicated in a diamond nano-particle slurry to embed diamond seed particles on the surface. The average crystal size in the diamond slurry was 5 nm. The diamond film was grown using hydrogen and methane as the source gases. During growth, the silicon wafer was maintained at 800° C. The pressure sensitivity of the sensor was precisely tuned in this step according to the application requirements.
Secondly, the backside of the silicon wafer was patterned and etched using deep reactive ion etching (DRIE). Each individual silicon wafer was formed into a tubular structure by etching through the entire 350 μm thickness of the wafer. The diamond layer on the front side of the silicon wafer was not affected by etching, and acted as an etch stop because of the large etch ratio difference between silicon and diamond layer.
Finally, an optical fiber was inserted into each tubular silicon housing defined by the DRIE process. For each housing, a single mode optical fiber with a diameter of 125 μm (SMF-28 Ultra, Corning) was first cleaved and cleaned to ensure particle free condition before the assembly. Then, the cavity inlet and the fiber were aligned using manual/piezo stages under microscopes. The alignment setup included two 5-axis high precision manual stages with attached piezo stages and two optical microscopes with CCD cameras positioned with 90-degree angle separation. The optical fiber was then carefully inserted into the housing structure while monitoring the gap distance between the cleaved fiber end the diamond diaphragm surface using the system described for use in sensor interrogation in Example 2. The cavity length was measured and controlled with a resolution of less than 1 nm by using the optical interrogation system. Horizontal position and tilt alignment were ensured by the clearance between the silicon housing and the inserted optical fiber. When a desired gap distance between the optical fiber and the diamond diaphragm was obtained, a small drop of UV curable adhesive (OP-5-20632, Dymax, Torrington, Conn.) was applied between the fiber and silicon cavity inlet to fix the fiber and seal the formed optical cavity. The gap between the cavity wall and the optical fiber was filled with adhesive by capillary effect. UV light from a spot light source was then exposed to the applied UV curable polymer securing the optical fiber to the cavity and sealing the air cavity near the end of the optical fiber. To minimize shrinkage of the UV curable polymer, a low intensity exposure (10% of the full intensity for 30 second) was applied followed by a high intensity exposure (100% of the full intensity for 60 second). The silicon structure holding the silicon housing structure was then broken off by applying minimal force. Additional ceramic adhesive (618-N-VFG, Aremco) was applied on top of the cross-linked UV curable polymer and thermally cured after 4 hours of air drying. Thermal curing was performed at 150° C. and 300° C. for 2 hours at each temperature.
The sensors from Example 1 were connected to a broadband optical interrogation system that included a 3 dB coupler (50:50 coupling ratio at λ=780 nm, Thorlabs, Newton, N.J.), a broadband spectrometer (flame-T, Ocean Optics, Largo, Fla.) with 0.4 nm wavelength resolution, and a broadband light source (HL-2000-HP, Ocean Optics). The spectrum position and the output of the reference sensor were collected by custom data acquisition code based on LabVIEW (National Instruments, Austin Tex.) while the chamber pressure and temperature were changed independently using a pressure regulator (Type 10, Bellofram Corp., Newell, W. Va.) and temperature controller (CN77332, Omega Engineering, Norwalk, Conn.) with a thermocouple (CO1-K, Omega Engineering) and two heaters (KH-103/10, Omega Engineering, Norwalk, Conn.). Frequency isolation using bandpass filtering and one peak tracing were used to monitor the optical cavity length change with high resolution. Additional details may be found in Bae et al. (2019), Miniature Diamond-Based Fiber Optic Pressure Sensor with Dual Polymer-Ceramic Adhesives, Sensors 19(9), 2202, which is hereby incorporated by reference as if fully set forth herein.
Pressure calibration of the sensor was conducted in a pressure chamber with a reference pressure sensor (MMG250V10P3C0T4A5CE, Omega Engineering Inc.) to quantify the changes in the sensor air cavity length with respect to the pressure changes. The calibration was performed in a pressure range of 2 to 9.5 psi. The calibration result is shown in
Pressure calibrations were performed at five different temperatures from 25 to 65° C. with 0.75 psi step size as shown in part (a) of
To evaluate the temperature sensitivity of the sensor, temperature calibration of the air cavity was performed. To measure the temperature sensitivity, the sensor was heated from 25 to 65° C. with an increment of 5° C. under the constant pressure of 2 psi. The cavity lengths were recorded at each temperature level. The obtained temperature calibration results are shown in part (b) of
To investigate the maximum operating temperature of the sensor, an additional temperature calibration was performed with a larger temperature range than the previous temperature calibration. For the calibration, the sensor was heated from 25° C. to 325° C. with an increment of 25° C. under the atmospheric pressure. The cavity lengths were recorded at each temperature level. A relatively linear relationship between air cavity length and temperature was observed up to 275° C., which is believed to be the maximum operating temperature of the sensor. This operating temperature was much higher than the glass transition temperature of the applied UV adhesive (78° C.).
Those skilled in the art will recognize that a wide variety of other modifications, alterations, and combinations can also be made with respect to the above described embodiments without departing from the scope of the invention, and that such modifications, alterations, and combinations are to be viewed as being within the ambit of the inventive concept.
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